Abstract
The dendron/dendrimer size was found to strongly influence properties of catalysts based on such macromolecules. Here, we assessed the dendritic effect of third generation pyridylphenylene dendrons (G3) immobilized on magnetic silica and loaded with Pd species in Suzuki-Miyaura reactions of Br-arenes and phenylboronic acid as compared with the second generation dendron (G2) based catalyst. A comprehensive analysis allows decoupling the dendron influence from other parameters identifying a strong positive dendritic effect (higher activity with G3 based composite), attributed to a larger available space and to a greater number of coordinating groups in the G3 to host reacting molecules and stabilize catalytic species. A “local Pd leaching” mechanism for the Suzuki-Miyaura reaction, which occurs in the dendron environment of the catalyst, provides an excellent catalytic activity. This finding along with easy magnetic separation (a remarkable catalytic stability in five consecutive catalytic cycles) make such systems promising for other cross-coupling reactions.
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•Strategy to functionalize the Fe3O4-SiO2 surface with G3 dendrons is developed.•Positive dendritic effect in catalysis is identified for G3 vs G2.•Excellent catalytic properties are observed in Suzuki-Miayura cross-coupling.